This invention relates to an electrolytic capacitor having a porous anodized pellet anode, a tri-metal can housing, and having a glass-metal hermetic seal, in which the can interior bears a thin layer of a ductile solderable metal extending from the mouth of the can to at most the bottom of the seal. The outer metal ring of the glass-metal seal is sealed to this layer, preferably by soldering.
In a glass-metal compression seal, the outer compression ring is made of a metal different than tantalum and has a coefficient of expansion which is about twice that of tantalum. In the past, the ring has been plated or clad with a metal clad resistant to corrosion by the electrlolyte used, frequently sulfuric acid.
Silver cathode cases have enjoyed popularity in tantalum capacitors, but migration of silver and plating out of silver on the anode from the cathode if reverse voltage is applied has been a serious problem. For this reason a tantalum case or one with a tantalum interior is preferred, but there have been problems in joining the seal ring to the tantalum case. It is to this problem that the present invention is addressed.